A new Stanford University School of Medicine study supports what vegetarians have been saying since the invention of the lentil loaf: A diet rich in vegetables, grains and legumes might be healthier for your heart than a conventional meat-based low-fat diet.

Published in yesterday's Annals of Internal Medicine, the study compares two low-fat diets, each containing identical amounts of saturated fat and cholesterol.

Participants who followed a vegetarian diet full of whole grains and nutrient-dense fruits and vegetables reduced their total and low-density lipoprotein (known as LDL, or "bad") cholesterol by more than twice as much as those who followed a more conventional low-fat diet that simply avoided saturated fat and cholesterol-rich foods.

Previous research has demonstrated that diets high in grains, fruits and vegetables help reduce cholesterol, but it was generally assumed that this was because these diets naturally contain less saturated fat and cholesterol than diets with more meat. In this study, all participants ingested the same amounts of saturated fat and cholesterol, no matter which diet they followed.

"We're frustrated that people are going out and getting SnackWell's cookies," says Christopher Gardner, an assistant professor of medicine at Stanford and the lead author of the study.

"We need a more positive message. Most studies say what to avoid. We want to say what you can include," he says.

The study involved 120 adults between the ages of 30 and 65 with moderately high levels of LDL. The roughly half who ate conventional low- cholesterol foods like turkey bologna sandwiches, Weight Watchers lasagna and low-fat chocolate chip cookies saw a 4.6 percent drop in LDLs. The group that ate the "plant-based" diet, with foods like bean burritos, sweet potato soup and oatmeal-carrot cookies, saw their LDL levels drop by 9.4 percent.

"This study confirms the 'power of plant chemicals,' " says Jo Ann Hattner, a nutrition consultant who teaches at Stanford. It "demonstrated that plant-based foods do have the power to lower LDLs."

For one month, participants could eat and drink only specially prepared meals, snacks and beverages. Both diets met the American Heart Association's dietary guidelines. For the study, the plant-based diet was meatless, yet Gardner, a 20-year vegetarian, points out that the AHA's definition of a heart- healthy diet does not have to be vegetarian.

"To add meat to a plant-based diet, you could have a Mediterranean salad and put slices of chicken on it, or you could put some meat in a stir-fry," he says.

Participants in the study were required to maintain an even weight and follow their normal exercise routine.

Hattner says the results are not surprising because there is already plenty of evidence that plant-based diets reduce cholesterol. She points out, however, that the relatively short length of the study might contribute to the dramatic results. "When you make a change in a diet, sometimes you might have a more immediate effect," she says.

Hattner says the study supports the new U.S. dietary guidelines' emphasis on whole grains and vegetables.

"As a nutritionist, I love to see these studies' results, as they provide science-based recommendations for the use of natural food sources to lower LDLs," says Hattner.